Surface treatment of titanium or



United States Patent SURFACE TREATMENT OF TITANIUM OR TITANIUM BASE ALLOYS Sidney Hands, Walsall, England, assignor to Chemical Industries Limited, poration of Great Britain N 0 Drawing. Application September 27, 1954, Serial No. 458,710

Imperial London, England, a cor- This invention relates to the treatment of titanium or titanium base alloy articles for the purpose of preparing an activated surface thereon prior to for example electroplating.

Titanium on exposure to air or other oxidising atmospheres forms a surface skin consisting chiefly of oxide, the complete removal of which to give a surface capable of receiving a good electrodeposited coating of another metal is not readily effected by standard pickling or etching compositions.

According to the present invention we provide a method of surface treatment of titanium or titanium base alloy articles prior to deposition of a coating metal thereon which comprises treating the surface of the said articles with concentrated hydrochloric acid solution at elevated temperature.

Preferably the treatment with the hydrochloric acid is effected at 90-100 C. The time of treatment depends upon the surface condition of the articles, thus at 90-100" C. it may vary from 5 to 15 minutes.

Under certain circumstances, for example in the case of heavily scaled material, it may be desirable to pretreat the article with a standard pickling solution, for example hydrofluoric acid/nitric acid solution, or with a standard caustic melt descaling bath consisting of molten sodium hydroxide with or without the addition of other constituents, before treatment with the hydrochloric acid.

By way of example, titanium rods to be silver-plated were immersed for 5-15 minutes in boiling commercial hydrochloric acid contained in an electrically heated glass vessel. They were then washed in hot water, rinsed in cold water, and thereupon transferred immediately to a standard plating bath containing silver nitrate, cyanide and potassium carbonate.

The method of the invention is particularly useful for the pretreatment of titanium surfaces which are to be electroplated, but it may also be used with advantage in cases Where an adherent coating of a metal is required to be applied by methods other than electrodeposition.

One application in which use of the method in accordance with the invention is of considerable benefit is in the cold drawing of titanium or titanium base alloy rod and wire. The effect of the high coeflicient of friction between titanium and the die materials can be overcome by plating the titanium with a metal having a lower coefiicient of friction as a lubricant-retaining layer, but with the electroplates obtainable on titanium by hitherto available methods it has been difiicult or impossible to obtain a degree of adhesion of the coating that would permit high speed drawing to thin gauges. However after preliminary pickling in boiling concentrated hydrochloric acid titanium rod can be plated with a suitable metal from conventional plating baths to give firmly adherent coatings enabling the drawing of fine gauge wire with greater ease and at far higher speed than hitherto possible.

I claim:

1. Method of surface treatment of titanium or titanium base alloy articles prior to deposition of a coating metal thereon, which comprises treating the surface of the said articles with concentrated hydrochloric acid solution at a temperature between C. and the boiling point of said solution.

2. Method in accordance with temperature is 90100 C.

3. Method in accordance with claim 1 in which the article is pretreated with a pickling bath of hydro-fluoric acid/nitric acid solution before treatment with the hydrochloric acid.

4. Method in accordance with claim 1 in which the article is pretreated with a descaling bath of molten sodium hydroxide before treatment with the hydrochloric acid.

5. Method in accordance with claim 1 in which the time of treatment is between 5 and 15 minutes.

potassium claim 1, in which the References Cited in the file of this patent UNITED STATES PATENTS 2,697,051 Mellgren Dec. 14, 1954 

1. METHOD OF SURFACE TREATMENT OF TITANIUM OF TITANIUM BASE ALLOY ARTICLES PRIOR TO DEPOSITION OF A COATING METAL THEREON, WHICH COMPRISES TREATING THE SURFACE OF THE SAID ARTICLES WITH CONCENTRATED HYDROCHLORIC ACID SOLUTION AT A TEMPERATURE BETWEEN 90* C. AND THE BOILING POINT OF SAID SOLUTION 